Rather than propose a
definition for intelligence, Howard
Gardner of Harvard offered a definition for an intelligence. "An
intelligence is the ability to solve problems, or to create products, that
are valued within one or more cultural settings" (Gardner, 1985, p.
x).

Gardner questioned the existence of "g" and wrote the
following:

While I do not question that some individuals may have the potential
to excel in more than one sphere, I strongly challenge the notion of
large general powers. To my way of thinking, the mind has the potential
to deal with several different kinds of content, but an individual's
facility with one content has little predictive power about his or her
facility with other kinds of content. In other words, genius...is likely
to be specific to particular contents: human beings have evolved to
exhibit several intelligences and not to draw variously on one flexible
intelligence. (Gardner, 1985, p. xi)

Much of his theory is based on work he had accomplished by studying
normal individuals whose brains have been injured (Gardner, 1982). Gardner
(1985) developed eight criteria for an intelligence:

potential isolation by brain damage

the existence of idiots savants, prodigies, and other exceptional
individuals

an identifiable core operation or set of operations

a distinctive developmental history, along with a definable set of
expert "end-state" performances

an evolutionary history and evolutionary plausibility

support from experimental psychological tasks

support from psychometric findings

susceptibility to encoding in a cultural symbol system

According to Gardner the brain supports at least seven different
abilities or intelligences. Each of these areas may develop relatively
independently of one another. Individuals may have strengths and
weaknesses and intelligences can be fashioned and combined in a
multiplicity of adaptive ways, each being relatively independent of the
others. The seven intelligences are linguistic, musical,
logical-mathematical, spatial, bodily-kinesthetic, interpersonal, and
intrapersonal (Gardner, 1985).

Gardner's multiple intelligence concept was not new. Truman Kelley
(1884-1961) published a book in 1928 entitled Crossroads in the Mind of
Man in which he criticized Spearman's model and set the stage for research
into "various broad multiple factors central to intelligence"
(Weiner & Stewart, 1984, p. 88).

Louis Thurstone
(1887-1955) and his students did much of the early work explaining a
multiple-factor theory. Zusne (1985) noted that Thurstone was the most
eminent psychometrician of his time. Thurstone was much more impressed
with the importance of clustering among subtests. With the aid of
statistical factor analytic techniques which he devised, and with wide
sampling of subtests, Thurstone discovered seven distinct clusters of
"Primary Mental Abilities" each of which he believed represented
an independent element of the intellect (Fancher, 1985).

Thurstone worked with his wife Thelma Gwinn Thurstone from 1924 to 1948
developing the Psychological Examinations and the Primary Mental Abilities
batteries. He moved to the University of North Carolina at Chapel Hill in
1952 . He died in 1955 and his wife completed some of his funded work at
the UNC Psychometics Laboratory (Bashaw & Bashaw, 1990).

As well as disagreeing with Spearman on a general factor of
intelligence, Kelley also disagreed with Thurstone on several points of
factor analysis. Kelley believed that the value of a given factor should
be included in any analysis so the importance of factors be considered. He
also felt the total variance of a correlation matrix should be used,
rather than just the common variance (Zusne, 1985).

When Thurstone applied his tests and analysis to children a second
order "g" factor emerged. Shouksmith (1970) reported that H.E.
Garrett used these findings to develop his developmental theory of
intelligence. Garrett found that correlations among test involving verbal,
numerical and spatial concepts became progressively lower as the age of
the sample increased from 8 to 18. He believed that "as a child
develops, so his or her abilities differentiate, and the functional
generality we find among tests at the younger age level, breaks down into
the quasi-independent factors quoted by Thurstone and his followers"
(p. 68). Shouksmith reported that the relationship between adults and
children was not as simple as Thurstone reported and noted that Anastasi
found similar discrepancies when comparing Army recruits and college
students.

J. P. Guilford
was responsible for "...[p]robably one of the most ambitious attempts
to simplify the factors within intelligence" (Weiner and Stewart,
1984, p. 89). Guilford called his work the structure-of-intellect model
and represented it by a three dimensional cube. Each dimension represents
a way to classifying intelligence. The following is Guilford's (1969)
description of the model"

One basis of classification is according to the basic kind of process
or operation performed...[a] second way of classifying the intellectual
factors is according to the kind of material or content involved...[w]hen
a certain operation is applied to a certain kind of content, as many as
six general kinds of products may be involved. There is enough evidence
available to suggest that, regardless of the combination of operations
and content, the same six kinds of products may be found associated. (p.
100-101)

Guilford's original model combined visual and auditory into a figural
content (Weiner & Stewart, 1984). According to Guilford,
"intelligence" is too complex to be covered by a few primary
mental abilities, much less by a single g-factor value or IQ score (Fancher,
1985).

Through the use of factor analysis, the California psychologist found
120 separate categories which defined the intellectual abilities that make
up one's intelligence. Guilford (1977) noted that " . . . [o]rdinary
IQ scales assess only a limited number of . . . [one's abilities], usually
those most important for learning in school . . . [and one ] may be high
in some, medium in others, and low in still others" (p. 13).

Although the concept of multiple intelligence or multiple facets of
intelligence is currently popular, there are theorists who support
Spearman's "g" factor. The most prominent among them is probably
Arthur Jensen who stated the following:

It is only when the concept of g is attributed meaning above and
beyond that derived from the factor analytic procedures from which it
gains its strict technical meaning that we run into the needless
argument over whether g is a unitary ability or a conglomerate of may
subabilities, each of which could be measured independently. We should
think of g as a "source" of individual differences in scores
which is common to a number of different tests. As the tests change, the
nature of g will also change. (p. 11)

Jensen (1980) included Spearman in a list of the three most influential
men in the testing movement and although he supported the "g"
factor of intelligence he noted that there are "also 'group factors'
that are common to groups of items...[and] items may be composed in such a
way as to measure g plus one or more group factors" (p. 128).

Jensen believed that the existence of "g" could not be
disproved and wrote the following regarding the existence of
"g":

Although psychologists can devise tests that measure only one group
factor, they cannot devise a test that excludes g....The ubiquitous
common factor to all tests is g, which has been aptly referred to as the
primary mental ability....And the same g permeates scholastic
achievement and many types of job performance, especially so-called
higher-level jobs. Therefore, g is most worthy of our scientific
curiosity. (Fancher, 1985, p. 159)

Robert Sternberg
introduced a three part theory of intelligence known as the triarchic
theory. Sternberg (1985) based his theory on the relationship between
intelligence and experience, the external world, and the internal world of
the individual.

The relationship with the internal world is academic smart, which is
what Sternberg said IQ tests usually measure (Trotter, 1986). This
encompasses his componential subtheory involving analytical thinking.
Being street smart involves his contextual subtheory. In this, one learns
how to manipulate the environment. The third type of intelligence covers
the experiential subtheory, which entails being a creative thinker. With
this, one is seeing old problems in new way.

Sternberg is currently developing the Sternberg Multidimensional
Abilities Test to assess the three intellectual strengths. One can only
wonder what future assessment instruments will evolve from this test, or
in what ways or in what situations the test will be used for which it was
not designed. Once again the mental measurement cycle begins. Many people
treat intelligence as if it were a physical substance like hair color or
height. One may have "x" amount of it while someone else has
"y" amount of it. Dr. Alexander Wesman of the Psychological
Corporation wrote:

We might better remember that it is no more reified than attributes
like beauty, or speed, or honesty. There are objects which are
classified as beautiful; there are performances which may be
characterized as speedy; there are behaviors which display honesty. Each
of these is measurable, with greater or less objectivity. Because they
can be measured, however, does not mean they are substances. We may
agree with E.L. Thorndike that if something exists it can be measured;
we need not accept the converse notion that if we can measure something
it has existence as a substance. (Winer & Stewart, 1984, p. 87)